FINISHING SECRETS . . .|
7. Using Wipe-On
Varnishes and Oils
A wipe-on varnish is an ideal finish for the woodturner. It is easy to apply, very forgiving, easy to repair, and gives the wood a durable protective film that is not easily damaged by water, food acids, body oils, or solvents. The only negative to using varnish as a wipe-on finish is the time that is required to build a high gloss surface film. The "blotchy" discoloration associated with varnish and oils is eliminated with the use of a sealer before the application. Discoloration, darkening and yellowing with age are the result of the resins and oils that are used, and this can be corrected to a large degree with selection of the varnish resins and oils that we use.
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As a straight oil finish, Tung Oil develops a hard surface that is waterproof, doesn't darken or turn yellow with age, and doesn't discolor the wood. But, it doesn't penetrate the surface very well, it takes forever to dry, and is more expensive than other oils. Partially polymerized Tung Oils solve the drying problem, and thinners can improve its penetration. However, these products are expensive and can cost as much as $30.00 for a quart. Linseed, soybean, and other vegetable oils offer faster drying and better penetration, but they also turn very dark with age, many become rancid, they are not as durable, and they must be periodically renewed. They are also are far less expensive than Tung Oil.
The Varnishes -- A Very Brief Summary
There are four types of varnish - alkyd, polyurethane, spar, and quick-drying. Any of these varnishes can be substituted whenever we mention "varnish" in this discussion.
Alkyds are the traditional varnishes made from a polyester resin. For a crude reference, think of polyester as the resin that is used in Fiberglass®. These varnishes are durable, flexible, resistance to abrasion, have good adhesion qualities, resistant to discoloration from UV and light, and are relatively less expensive than the other varnishes. Their only negative is that they are very slow drying and will take 24-hours to dry sufficiently for recoating. For this reason alone, the alkyd varnishes are becoming difficult to find as a furniture finish, but their superior qualities make them the choice for floor finishing varnishes.
Polyurethane resins have replaced the alkyds for only one reason - they dry and cure faster. They are also more water resistant. But, several of the benefits of the alkyds have been sacrificed. Polyurethane varnishes are not light and UV resistant, and therefore will turn "yellow" rather quickly. They can also have adhesion problems with themselves and other finishes..
Spar varnish is a formulation of phenolic and alkyd resins in Tung Oil. Another crude comparison would liken phenolic resin to Bakelite®, waterproof, and very hard. Spar varnish is a relatively hard finish with superior water resistance and flexibility. It has a good resistance to damage from either acid or alkali substances or deterioration from light and UV. Unfortunately, it is very slow drying and it has a naturally deep yellow color.
Fast-drying, or VT, varnishes have been modified with styrene resins to produce a very fast drying time that is similar to that of a nitrocellulose lacquer. This speed comes with the sacrifice of the protective properties found in the other varnishes.
It should be obvious from a comparison of the properties of the various varnishes that we should be using either alkyd or spar for our woodturnings. Either will offer the flexibility to move with the wood as it changes with seasonal moisture changes, and provide the durable surface protection required for an item that will see frequent handling over a period of many years. Although I have preferred the alkyd varnishes for many years, it has become difficult to find as a furniture finishing product. However, it is readily available as a floor finish, but usually in nothing less than a 1-gallon container. I started using spar several years ago because it was easier to find. I have not found it to be superior to the alkyd as a finish for turned wood.
Many woodturners prefer the higher gloss from fewer coats and faster drying of the polyurethane varnishes. I don't use them because I don't like their plastic appearance. They may be faster drying, but adhesion can be a problem, and they turn yellow and deteriorate with age and exposure to light. The manufacturers have added a variety of ingredients in an attempt to solve these problems, but they have only succeeded in reducing them while increasing their cost.
These finishes have been promoted as "the answer" to our wood finishing problems. Gel finishes are the polyurethane varnish resins without the liquid solvents. These are the solids that will settle to the bottom of a can of poly-varnish. These finishes will give a more uniform surface coloring because they do not penetrate as deeply into the end grain as the liquid varnishes. Other than that, they have all of the same characteristics associated with any other polyurethane varnish. Bartley'sŇ and General FinishesŇ are the most recognized brand names.
Wipe-On Varnish Finishes
Our preference should be a varnish based finish that can be applied with either a rag or a paper towel, rather than by a brushing or spray application. Any varnish can be used as a wipe-on finish with the addition of 50% thinner. The addition of oil will help it flow out into a thin uniform coat. The amount of oil will influence the flexibility of the final surface finish and the drying time of the finish, more oil is more flexible and takes longer to dry. If too much oil is used the finish will be soft.
The quantity of oil in the finish is often referred to as being a long, short, or medium oil finish. Commercial varnishes as they come from the can are a "medium oil" varnish with about 50% oil. A typical wiping varnish is a "very long oil" varnish with 75% oil.
The oils that can be added to the finish are discussed in the previous Article No. 6 in this series.
Commercial Oil/Varnish Products
We will begin this discussion with the commercial products because they are where most woodturners go for this type finish.
Regardless of their advertising claims, all of these commercial finishes are the same - a mixture of varnish resins, some type of oil, and thinner. Danish oil doesn't have the varnish resins. Most manufacturers have sacrificed finish quality for a product that is easy to use and fast drying. Most of them have added metallic drying agents to increase their cure time, and compensate for vegetable oils that are not a natural "drying oil". All of them contain a very large amount of thinner and a relatively small quantity of varnish and oil.
Although the manufacturers recognize the superior qualities of Tung Oil in a finish, many do not contain any Tung Oil at all. Regardless of their labeling, "Tung Oil Finish" has become a generic term for any oil finish. I have heard claims from other woodworkers that some of these do contain Tung Oil, but absent any list of ingredients on the label, I can only assume that they do not. There is nothing wrong with these products if they will produce an acceptable finish for you. I object to the false advertising and labeling, and prefer to not use anything with "secret" ingredients.
I can recommend the following commercial products on the basis of personal experience. There may be others in the marketplace that just as good, but I have yet to find them.
- Daly's Sea-Fin Teak Oil® is a Tung Oil finish that is widely available in the Northwest. In recent years their distribution has increased, so it may be available in other areas. In my opinion, it is the best of the commercial wipe-on products. It is easy to get a good finish when the directions printed on the label are followed.
- Waterlox® is a nationally available Tung Oil product that is similar to Sea-Fin. It is generally available only through the mail-order catalogs. It is available as either the "Original" or as a "Marine" finish. Other than the "Marine" costing $10 more per gallon, I have never found any difference between them. Buy the "Original" because it is cheaper.
- Gillespie's Tung Oil Finish® is an excellent Tung Oil finish that is not quite as good (personal opinion) as Sea-Fin or Waterlox, but it is usually available at most paint specialty stores, Home Depot, Lowe's, and similar retailers. stores.
- Hope's Tung Oil Finish® is an excellent product that I have not used for several years because it is difficult to find, and when I have, the stock was very old. If you can locate fresh stock, try it. You will be pleased with the results.
- Watco® Teak Oil Finish, in the can with the blue label. While it is a Linseed Oil finish with UV inhibitors added, its finishing properties are considerably different from the more familiar Watco Danish Oil in the can with the brown label. If you have sworn-off on Watco® products because of things you have heard, or have had bad experiences with them, then try this one. I think that you will like it. Even the Danish Oil has improved since ownership by Flecto has returned it to its original formula.
There are several products sold under the name "Danish Oil". The most common is the Watco® product in the brown can, but there are other similar products available. These are an oil (only) finish that is made from linseed, soybean, and other oils, a lot of thinner, and no varnish resins. Since they contain no varnish resins, Danish Oils will not build a surface film, and any film that will form is incidental to the amount of linseed oil that is present.
While Danish Oils are fast and easy to apply and have many other uses for our finishing, they are not a good final finish for our turned wood. The finish is soft, not very durable, and will require rejuvenation every couple years when exposed to even indirect sunlight.
It is interesting to note that there is nothing "Danish" in these finishes. They are an oil finish that was marketed as a way for us to duplicate the finish on the "Danish Modern" furniture style that was popular at the time, which was a lacquer.
My Home-Brew Oil/Varnish Finish
I mix my own oil/varnish because I have control of the ingredients, it is always fresh, and it is less expensive to use than commercial products that contain less than 20% finishing solids. $35.00 a gallon is a lot to pay for something that is 80% mineral spirits or other thinners. My opinion may be somewhat biased because I learned to mix my own finishes before any of the commercial mixtures were available.
I use a mixture of equal parts 100% pure Tung Oil, Varnish, and Turpentine. The proportions aren't critical. If there is any error in the proportions, it should be towards a lesser amount of oil, and a greater quantity of thinner. Additional oil will improve its wiping properties, but it will also increase its drying time.
In my opinion, McCloskey's "Man'O War" Gloss Spar Varnish (in the red can) is the best varnish on the market for turned wood. It has all of the benefits of a spar varnish because of its Tung Oil, phenolic, and alkyd resins. Its only disadvantage is that it is more expensive than other varnishes. I have always preferred the traditional alkyd varnishes for furniture and turned wood, but they are getting difficult to find, and I have limited experience with the floor finishes mentioned earlier.
Pure Gum Spirits of Turpentine are used for the thinner because the natural oils become a part of the finish and enhance the qualities of the varnish. Other thinners do not become a part of the finish. Turpentine substitutes are nothing more than an expensive form of Mineral Spirits (paint thinner) that evaporates more slowly.
Either 1-K kerosene, VM&P Naptha, or Mineral Spirits can be substituted for the turpentine. Naptha dries faster than Turpentine, Kerosene dries slower and mineral spirits dries only slightly faster, but also gives the mixture a shorter shelf life. None of them impart anything to the finish. The new odorless Mineral Spirits is not "odorless" and it is more expensive.
I use whatever good quality 100% Tung Oil is available at the local paint store because I like to inspect the cans for signs of aging before buying. Old Master's® and Hope's® are the brands usually available, and both are good quality. Boiled Linseed Oil can be used, but the resulting finish is softer and it will become darker faster than with Tung Oil. Changing the oil that is used to a 50/50 mixture of Tung Oil and Boiled Linseed Oil seems to better enhance the grain in highly figured wood such as Maple.
The wipe-on, wipe-off, wait, buff with steel-wool, and repeat, application is familiar to nearly all woodturners who have ever used a commercial finishing product such as Watco Danish Oil.
For wipe-on application, a "finishing-ball" is easier to use than a paper towel, and it doesn't fall apart. Prepare the ball by making a golf ball sized wad of cheesecloth, and then wrapping it in a 6" square of cotton cloth. A sheet of paper towel that has been folded into as small a square as possible can substitute for the cheesecloth.
A paper towel works well for small projects, and Viva is the softest and most lint free that I have used. I fold the towel twice in the long direction, and then roll it as tight as possible to make an applicator that will keep my fingers out of the finish.
The directions for application are simple:
- Apply a heavy coat of finish and keep it wet for several minutes. Sand the first coat with 400-grit wet-dry, and the second with 600-grit, to form a slurry that will act as a grain filler. Add more finish as it starts to dry. Sanding is omitted after the second coat.
- Wait a few minutes until it becomes tacky.
- Remove all of the finish with a soft cloth or paper towel.
- Wait overnight.
- Buff it back with steel wool
- Repeat Steps 1 through 5 as many times as required to achieve the desired gloss. I apply as many coats as needed to leave a glossy finish after waiting overnight, 5 or 6 depending on the wood, and then add one more.
Wet Sanding Application
An alternative application is sanding with wet/dry paper while the piece is spinning on the lathe, using the finish as the lubricant. I dry-sand through about 150-grit, and then wet-sand starting at 180-grit and continue through 600-grit. Wipe the slurry from the wood surface before going on to the next finer grade. When you are done sanding you are done finishing. Let it dry overnight and buff with steel wool.
This works very well for small articles - weed-pots, vases, etc. After dry sanding, submerge the piece in a container of the finishing liquid for at least 1-hour or until it is saturated. Allow it to drip dry. Set it aside for several days until the finish is completely dry. If necessary, wipe off any excess that refuses to dry. Then buff it with a soft linen wheel that has been charged with a little Tripoli compound, followed with a wax buffing. The buffing wheels that are specifically made for wood finishing are the best. However, any hardware store cotton wheel can be used when nothing else is available. I always recommend using one of these first, then ordering the expensive wheels from Craft Supplies after determining that you want to continue using this finishing method.
A suitable mixture for this type of finish application can be made from 1-gallon Boiled Linseed Oil, 2-gallons Turpentine or Paint Thinner (Mineral Spirits), and 1- quart varnish. Use equivalent smaller quantities if you don't to make it in a five-gallon bucket. Add ˝-cup of Japan Drier if you want it to cure faster when the shop temperatures are below 65°F at night. This is not an ideal finish, but it is inexpensive, and just a good as Watco or other Danish Oils. It is also an excellent preservative finish that is better than anything commercially available for wood decks and outdoor furniture.
I use this method for finishing large pieces that are turned from Western Red Cedar and Redwood burls. The wood is turned to its final form and thickness and rough sanded while it is still wet. Then it is placed in a tub filled with enough of the home-brew mixture to cover the wood, and left to soak until all of the water in the wood has been replaced with the mixture. This may take several days or several weeks. Then the piece is removed from the tub and set aside until the "finish" in the wood has cured. Again, this will also take several weeks. When all of this has dried, the wood is put back in the lathe given a final sanding, and the bottom is finished. A higher gloss can be brought out with a buffing wheel.
I don't use any of these finishes because I don't like the results and because they are constantly changing. These finishes could have a lot to offer. They could solve many of the problems that are associated with traditional varnishes and oils because they penetrate well, do not discolor the wood, and have a hard durable surface film that is clear and will not change color with age.
However, waterborne finishes have a "bluish" tint and poor reflective qualities that leave the wood with a "muddy" appearance. And, they will not enhance the wood grain like an oil. They will raise the grain, but that is a minor problem. The manufacturers have added soluble oils and other ingredients to reduce the effects of these problems and make them behave more like the traditional finishes. So far, they have not been successful (my opinion). Meanwhile, the products are constantly changing as the manufacturers change their formulations, making it difficult to get consistent results from inconsistent products.
The manufacturers have created another problem for themselves by calling their waterborne products by the same names as the traditional finishes. Then they have taken on the task to make them behave the same when they are not and never will be. Some brands have disguised the fact that their product is waterborne, and we have to read the fine print on the back of the can to determine that water is actually used for clean-up.
© 2002 - 2009 by Russ Fairfield. All rights reserved.
No parts of this publication may be reproduced in any form
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